Adfu is a web ad server that Cmdrtaco and Nate wrote when they decided they didn't want to pay Doubleclick a bunch of money. It's serving the ad that you see above, as well as (more impressively) all the ads on Slashdot. As soon as we're done with our current level of tinkering, we're going to release the source code under the GPL, so geek Web Entrepreneurs can be like us.